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Hybrid application

A hybrid application is one that listens for requests from two or more different sources. This can combine an HTTP server with a microservice listener or even just multiple different microservice listeners. The default createMicroservice method does not allow for multiple servers so in this case each microservice must be created and started manually. In order to do this, the INestApplication instance can be connected with INestMicroservice instances through the connectMicroservice() method.

const app = await NestFactory.create(AppModule);
const microservice = app.connectMicroservice<MicroserviceOptions>({
  transport: Transport.TCP,
});

await app.startAllMicroservices();
await app.listen(3001);

Hint the app.listen(port) method starts an HTTP server on the specified address. If your application does not handle HTTP requests then you should use the app.init() method instead.

Notice The order of these calls matters. With await app.startAllMicroservices() first (as above), the microservices begin consuming messages before the application's lifecycle hooks (such as onModuleInit and onApplicationBootstrap) have completed. Call app.listen() (or app.init()) before startAllMicroservices() if your handlers must not receive messages until every module has fully initialized.

To connect multiple microservice instances, issue the call to connectMicroservice() for each microservice:

const app = await NestFactory.create(AppModule);
// microservice #1
const microserviceTcp = app.connectMicroservice<MicroserviceOptions>({
  transport: Transport.TCP,
  options: {
    port: 3001,
  },
});
// microservice #2
const microserviceRedis = app.connectMicroservice<MicroserviceOptions>({
  transport: Transport.REDIS,
  options: {
    host: 'localhost',
    port: 6379,
  },
});

await app.startAllMicroservices();
await app.listen(3001);

To bind @MessagePattern() to only one transport strategy (for example, MQTT) in a hybrid application with multiple microservices, we can pass a second argument identifying the transport. For the built-in strategies, this is a value of the Transport enum; for a custom transporter, it is the transportId symbol of its server class.

@MessagePattern('time.us.*', Transport.NATS)
getDate(@Payload() data: number[], @Ctx() context: NatsContext) {
  console.log(`Subject: ${context.getSubject()}`); // e.g. "time.us.east"
  return new Date().toLocaleTimeString(...);
}
@MessagePattern({ cmd: 'time.us' }, Transport.TCP)
getTCPDate(@Payload() data: number[]) {
  return new Date().toLocaleTimeString(...);
}
@MessagePattern('topic.time.us', XYZServer.Transport) // XYZServer is a custom transporter
getXYZDate(@Payload() data: number[]) {
  return new Date().toLocaleTimeString(...);
}

@Bind(Payload(), Ctx())
@MessagePattern('time.us.*', Transport.NATS)
getDate(data, context) {
  console.log(`Subject: ${context.getSubject()}`); // e.g. "time.us.east"
  return new Date().toLocaleTimeString(...);
}
@Bind(Payload(), Ctx())
@MessagePattern({ cmd: 'time.us' }, Transport.TCP)
getTCPDate(data, context) {
  return new Date().toLocaleTimeString(...);
}

@Bind(Payload())
@MessagePattern('topic.time.us', XYZServer.Transport)
getXYZDate(data) {
  return new Date().toLocaleTimeString(...);
}

Hint@Payload(), @Ctx(), Transport and NatsContext are imported from @nestjs/microservices. XYZServer.Transport here stands for the transportId symbol exposed by the custom transporter.

Sharing configuration#

By default a hybrid application will not inherit global pipes, interceptors, guards and filters configured for the main (HTTP-based) application. To inherit these configuration properties from the main application, set the inheritAppConfig property in the second argument (an optional options object) of the connectMicroservice() call, as follow:

const microservice = app.connectMicroservice<MicroserviceOptions>(
  {
    transport: Transport.TCP,
  },
  { inheritAppConfig: true },
);